5,569 research outputs found
Investigation of the aerodynamic characteristics of a lifting body in ground proximity
The use of cambered hull shapes in the next generation of lighter-than-air vehicles to
enhance aerodynamic performance, together with optimized take-off manoeuvre profiles,
will require a more detailed understanding of ground proximity effects for such aircraft. A
series of sub-scale wind tunnel tests at Re = 1.4 x 106 on a 6:1 prolate spheroid are used to
identify potential changes in aerodynamic lift, drag and pitching moment coefficients that
are likely to be experienced on the vehicle hull in isolation when in close ground proximity.
The experimental data is supported by a preliminary assessment of surface pressure changes
using a high order panel method (PANAIR) and RANS CFD simulations to assess the flow
structure. The effect of ground proximity, most evident when non-dimensional ground
clearance (h/c) < 0.3, is to reduce lift coefficient, increase drag coefficient and increase the body pitching moment coefficient
Quantum Critical Behavior in Kondo Systems
This article briefly reviews three topics related to the quantum critical
behavior of certain heavy-fermion systems. First, we summarize an extended
dynamical mean-field theory for the Kondo lattice, which treats on an equal
footing the quantum fluctuations associated with the Kondo and RKKY couplings.
The dynamical mean-field equations describe an effective Kondo impurity model
with an additional coupling to vector bosons. Two types of quantum phase
transition appear to be possible within this approach---the first a
conventional spin-density-wave transition, the second driven by local physics.
For the second type of transition to be realized, the effective impurity model
must have a quantum critical point exhibiting an anomalous local spin
susceptibility. In the second part of the paper, such a critical point is shown
to occur in two variants of the Kondo impurity problem. Finally, we propose an
operational test for the existence of quantum critical behavior driven by local
physics. Neutron scattering results suggest that CeCuAu passes this
test.Comment: 6 pages, 4 eps figures, REVTeX (epsf style
The ‘Burgundian’ hat from Herjolfsnes, Greenland: new discoveries, new dates
In 1921, during Poul Nørlund’s excavation at the Norse farm Herjolfsnes, Greenland, a tall hat was recovered from the burial grounds surrounding the farm’s church, where a substantial collection of medieval garments had been recovered. This unusual hat came to symbolize not only the end of the Greenland Norse colony but also its enduring cultural links with continental European fashions, following a comment to this effect published by Nørlund himself. In 1996, the hat was dated to the early fourteenth century by Arneborg, a century earlier than Nørlund’s dating, based on stylistic comparisons with European examples. Recent research on North Atlantic textiles led to a reexamination of the hat, with different sections sampled and resubmitted for accelerated mass spectrometry dating. The results suggest that the body of the hat and its crown are of different periods with c. 100 years between them. This reanalysis of the Herjolfsnes ‘tall brimless hat’ or ‘Burgundian’ hat suggests that a considerable amount of cloth recycling took place in these North Atlantic colonies, that cloth was a valued and cherished commodity, and raises questions about the role this item of material culture role should play in discussions of identity and enduring links between Greenland and the continent
Dorset, Norse, or Thule? Technological transfers, marine mammal contamination, and AMS dating of spun yarn and textiles from the Eastern Canadian Arctic
Source at https://doi.org/10.1016/j.jas.2018.06.005.Yarn and textiles recovered from prehistoric Dorset and Thule culture sites in the Eastern Canadian Arctic have raised questions about the extent and timing of indigenous and Norse interaction in the New World, whether the yarn represents technological transfers between Greenland's Norse settlers and the Dorset, or whether these Indigenous Arctic groups had independent fiber technologies before contact with Europeans. However, the extensive use of marine mammals in northern cultural contexts, and the penetration of oils from these animals' tissues into datable terrestrial materials, has posed general problems for reliably dating sites in the Arctic and has raised questions specifically about previous efforts to date these fiber objects. In this paper, we use a recently developed protocol for removing marine mammal organic contaminants entirely from radiocarbon samples, making AMS dating possible and reliable for Arctic research. This study uses those protocols to directly date a suite of woven and spun animal fiber artifacts from five Dorset and Thule archaeological sites in the eastern Canadian Arctic. Directly dating these artifacts with marine mammal oils removed helps to answer questions about Norse contact with Dorset and Thule communities, sheds new light on the topic of indigenous fiber technologies in the North, and raises new questions about European contacts with the people of the North American Arctic prior to sustained efforts at colonization after the 18th century
Foreign investment in the Los Angeles real estate market
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1987.Bibliography: leaves 87-89.by Michael J. Smith and Kevin P. Whalen.M.S
Effects of drinking-water filtration on Cryptosporidium Seroepidemiology, Scotland
Continuous exposure to low levels of Cryptosporidium oocysts is associated with production of protective antibodies. We investigated prevalence of antibodies against the 27-kDa Cryptosporidium oocyst antigen among blood donors in 2 areas of Scotland supplied by drinking water from different sources with different filtration standards: Glasgow (not filtered) and Dundee (filtered). During 2006–2009, seroprevalence and risk factor data were collected; this period includes 2007, when enhanced filtration was introduced to the Glasgow supply. A serologic response to the 27-kDa antigen was found for ≈75% of donors in the 2 cohorts combined. Mixed regression modeling indicated a 32% step-change reduction in seroprevalence of antibodies against Cryptosporidium among persons in the Glasgow area, which was associated with introduction of enhanced filtration treatment. Removal of Cryptosporidium oocysts from water reduces the risk for waterborne exposure, sporadic infections, and outbreaks. Paradoxically, however, oocyst removal might lower immunity and increase the risk for infection from other sources
Cocaine surface contamination and the medico-legal implications of its transfer
AbstractThe question posed by this research involves how frequently one can expect to contact cocaine in day-to-day living experiences where drug use may not normally be suspected. Issues concerning contamination are germane to medico-legal investigators who evaluate the significance of drug test results in (1) questioned deaths, (2) public health concerns, (3) drugs crimes, and (4) drug use toxicological tests potentially caused by external contamination, such as hair, sweat, and skin swabs. Previous surface studies focus mainly on currency drug contamination; few have addressed other common surfaces.Public surfaces handled by a large number of people, such as building entrance door handles, bank currency dispensing machines, food store shopping carts, and service station fuel pumps within the New Haven, Connecticut metropolitan area were tested. Socio-economically, the distribution of items tested ranged from working-class to upper-middle class areas. Results were obtained using the Securetec Drugwipe II® which is an immunological, on-site test device. Precautions were taken to avoid carry-over and other potential contamination from handling including single-use latex gloves which were pre-tested as a negative control immediately before swabbing. Analysis was performed according to the manufacturer’s instructions and in the laboratory to standardize conditions. Drugwipe II® limit of detection (LOD) is ∼50ng.Test results revealed 78% positive for cocaine substances as follows: fuel pump buttons for credit card authorization, 100% positive (n=10 individual locations); ATM machines for currency withdrawal, 100% positive (n=10 individual locations); grocery store shopping carts, 70% positive; academic building entrance doors, 30% positive (n=10); and shopping mall entrance/exit doors, 100% positive (n=5).Forensic scientists and medico-legal investigators responsible for interpreting surface test results are cautioned to consider contamination before ascribing drug activity to a specific individual. For legal proceedings these results are indicative but not conclusive because immunological tests are considered presumptive and may react with the parent substance (cocaine), related compounds (benzoylecgonine, ecgonine methyl ester, ecgonine, nor-ecgonine, and cocaethylene) and immunologically similar materials
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Atmospheric chemistry of C4F9OC2H5 (HFE-7200), C4F9OCH3 (HFE-7100), C3F7OCH3 (HFE-7000) and C3F7CH2OH: temperature dependence of the kinetics of their reactions with OH radicals, atmospheric lifetimes and global warming potentials
The atmospheric chemistry of several gases used in industrial applications, C4F9OC2H5 (HFE-7200), C4F9OCH3 (HFE-7100), C3F7OCH3 (HFE-7000) and C3F7CH2OH, has been studied. The discharge flow technique coupled with mass-spectrometric detection has been used to study the kinetics of their reactions with OH radicals as a function of temperature. The infrared spectra of the compounds have also been measured. The following Arrhenius expressions for the reactions were determined (in units of cm3 molecule-1 s-1): k(OH + HFE-7200) = (6.9+2.3-1.7) × 10-11 exp(-(2030 ± 190)/T); k(OH + HFE-7100) = (2.8+3.2-1.5) × 10-11 exp(-(2200 ± 490)/T); k(OH + HFE-7000) = (2.0+1.2-0.7) × 10-11 exp(-(2130 ± 290)/T); and k(OH + C3F7CH2OH) = (1.4+0.3-0.2) × 10-11 exp(-(1460 ± 120)/T). From the infrared spectra, radiative forcing efficiencies were determined and compared with earlier estimates in the literature. These were combined with the kinetic data to estimate 100-year time horizon global warming potentials relative to CO2 of 69, 337, 499 and 36 for HFE-7200, HFE-7100, HFE-7000 and CF3CF2CF2CH2OH, respectively
On Optimizing the Conditional Value-at-Risk of a Maximum Cost for Risk-Averse Safety Analysis
The popularity of Conditional Value-at-Risk (CVaR), a risk functional from
finance, has been growing in the control systems community due to its intuitive
interpretation and axiomatic foundation. We consider a non-standard optimal
control problem in which the goal is to minimize the CVaR of a maximum random
cost subject to a Borel-space Markov decision process. The objective takes the
form , where is a
risk-aversion parameter representing a fraction of worst cases, is a
stage or terminal cost, and is the length of a finite
discrete-time horizon. The objective represents the maximum departure from a
desired operating region averaged over a given fraction of worst
cases. This problem provides a safety criterion for a stochastic system that is
informed by both the probability and severity of the potential consequences of
the system's trajectory. In contrast, existing safety analysis frameworks apply
stage-wise risk constraints (i.e., must be small for all , where
is a risk functional) or assess the probability of constraint violation
without quantifying its possible severity. To the best of our knowledge, the
problem of interest has not been solved. To solve the problem, we propose and
study a family of stochastic dynamic programs on an augmented state space. We
prove that the optimal CVaR of a maximum cost enjoys an equivalent
representation in terms of the solutions to this family of dynamic programs
under appropriate assumptions. We show the existence of an optimal policy that
depends on the dynamics of an augmented state under a measurable selection
condition. Moreover, we demonstrate how our safety analysis framework is useful
for assessing the severity of combined sewer overflows under precipitation
uncertainty.Comment: A shorter version is under review for IEEE Transactions on Automatic
Control, submitted December 202
Protein associated with SMAD1 (PAWS1/FAM83G) is a substrate for type I bone morphogenetic protein receptors and modulates bone morphogenetic protein signalling
Bone morphogenetic proteins (BMPs) control multiple cellular processes in embryos and adult tissues. BMPs signal through the activation of type I BMP receptor kinases, which then phosphorylate SMADs 1/5/8. In the canonical pathway, this triggers the association of these SMADs with SMAD4 and their translocation to the nucleus, where they regulate gene expression. BMPs can also signal independently of SMAD4, but this pathway is poorly understood. Here, we report the discovery and characterization of PAWS1/FAM83G as a novel SMAD1 interactor. PAWS1 forms a complex with SMAD1 in a SMAD4-independent manner, and BMP signalling induces the phosphorylation of PAWS1 through BMPR1A. The phosphorylation of PAWS1 in response to BMP is essential for activation of the SMAD4-independent BMP target genes NEDD9 and ASNS. Our findings identify PAWS1 as the first non-SMAD substrate for type I BMP receptor kinases and as a novel player in the BMP pathway. We also demonstrate that PAWS1 regulates the expression of several non-BMP target genes, suggesting roles for PAWS1 beyond the BMP pathway
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